std::println

 

C++

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Print functions

print (C++23)

println (C++23)

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Defined in header <print>
template< class... Args >   void println( std::FILE* stream,                 std::format_string<Args...> fmt, Args&&... args );	(1)	(since C++23)
template< class... Args >   void println( std::format_string<Args...> fmt, Args&&... args );	(2)	(since C++23)

Format args according to the format string fmt with appended '\n' (which means that each output ends with a new-line), and print the result to a stream.

1) Equivalent to:

std::print(stream, "{}\n", std::format(fmt, std::forward<Args>(args)...));

2) same as (1) when stream is equal to the standard C output stream stdout, i.e.

std::println(stdout, fmt, std::forward<Args>(args)...);

The behavior is undefined if std::formatter<Ti, char> does not meet the BasicFormatter requirements for any Ti in Args (as required by std::make_format_args).

Parameters

stream	-	output file stream to write to
fmt	-	an object that represents the format string. The format string consists of ordinary characters (except { and }), which are copied unchanged to the output, escape sequences {{ and }}, which are replaced with { and } respectively in the output, and replacement fields. Each replacement field has the following format: { arg-id (optional) } (1) { arg-id (optional) : format-spec } (2) 1) replacement field without a format specification 2) replacement field with a format specification arg-id - specifies the index of the argument in args whose value is to be used for formatting; if it is omitted, the arguments are used in order. The arg-id s in a format string must all be present or all be omitted. Mixing manual and automatic indexing is an error. format-spec - the format specification defined by the std::formatter specialization for the corresponding argument. Cannot start with }. For basic types and standard string types, the format specification is interpreted as standard format specification. For chrono types, the format specification is interpreted as chrono format specification. For range types, the format specification is interpreted as range format specification. For std::pair and std::tuple, the format specification is interpreted as tuple format specification. For std::thread::id and std::stacktrace_entry, see thread id format specification and stacktrace entry format specification. For std::basic_stacktrace, no format specifier is allowed. (since C++23) For std::filesystem::path, see path format specification. (since C++26) For other formattable types, the format specification is determined by user-defined formatter specializations.
args...	-	arguments to be formatted

Return value

(none)

Exceptions

• std::bad_alloc on allocation failure.
• std::system_error, if writing to the stream fails.
• Propagates any exception thrown by used formatters, e.g. std::format_error.

Notes

Feature-test macro	Value	Std	Feature
__cpp_lib_print	202207L	(C++23)	Formatted output
__cpp_lib_format	202207L	(C++23)	Exposing std::basic_format_string

Example

Run this code

#include <print>
 
int main()
{
    // Each call to std::println ends with new-line
    std::println("Please");
    std::println("enter");
 
    std::print("pass");
    std::print("word");
 
    std::println(""); // same effect as std::print("\n");
}

Output:

Please
enter
password

See also

print (C++23)	prints to stdout or a file stream using formatted representation of the arguments (function template)
println(std::ostream) (C++23)	outputs formatted representation of the arguments with appended '\n' (function template)
format (C++20)	stores formatted representation of the arguments in a new string (function template)
printffprintfsprintfsnprintf (C++11)	prints formatted output to stdout, a file stream or a buffer (function)